The use of abrasive tools for cutting glass or crystal articles is generally designed to detach from the actual article the mass of glass or crystal, hereinafter referred to as the moil, which was used for holding the article while it was being shaped by plastic deformation while hot.
The use of abrasive tools for trimming glass or crystal ware is the operation which follows the cutting stage and is generally intended to finish the edge left on the article by the cutting operation.
Conventionally, the abrasive tool cutting of glass or crystal articles is performed by means cf an abrasive disc, the axis of rotation of which is situated in a substantially vertical plane, the article being so positioned that the anticipated cutting plane coincides with the plane of symmetry of the abrasive disc. Generally, the article is set on its base on a substantially horizontal plane, the upper part of the mass of glass or crystal constituting the article to be cut constituting the part hereinabove defined as being the moil or cullet, the bottom part of the glass or crystal mass constituting the article to be cut actually representing the article proper.
Cutting glass or crystal articles with abrasive tools is likewise conventionally performed by means of an abrasive disc, the axis of rotation of which is situated in a substantial-y horizontal plane, the article being so positioned that the anticipated cutting plane coincides with the plane of symmetry of the abrasive disc. Generally, the article is held by a device in such a way that its base is situated in a substantially vertical plane.
Cutting glass or crystal articles with abrasive tools is likewise conventionally performed by means of two abrasive discs working substantially at the same time and penetrating the article to be cut according to identical movements. In this case, the axis of rotation of the abrasive discs is generally in a substantially vertical plane and the article is generally set on its base on a substantially horizontal plane, the upper part of the mass of glass or crystal constituting the article to be cut constituting the part which is hereinabove defined as being the moil, the lower part of the mass of glass or crystal constituting the article to be cut representing the article proper.
Whichever is the geometrical configuration chosen, the sequence of operations is identical. Firstly, the disc or discs, rotating at high speed, will slowly approach the article which is stationary and will penetrate the article to a suitable depth, that is to say if the article is solid then it will penetrate sufficiently close to the center or if the article is hollow then it will penetrate it sufficiently that the edge of the abrasive disc will break through into the central cavity, when penetration is considered as complete. Secondly, the article is caused to rotate slowly so that during the course of this rotation the abrasive disc cuts a furrow into the mass of glass or crystal, which finally results in the moil becoming detached from the useful part of the article. The slow rotation of the article may already have begun while the abrasive disc is still in the process of penetrating the article.
When only one disc being used, the path followed by the disc during penetration into the article may be substantially radial, which, for a given article, corresponds to the least displacement of the abrasive disc; on the other hand, if a single disc is performing the cutting operation, the article will be required to make a rotation of about 360.degree. in order to be cut through completely.
According to the conventional method of cutting, using an abrasive disc having an axis of rotation which is substantially vertical, the moil is above the cutting disc during the cutting process, which makes it necessary to hold it manually or to use some device to support the moil and keep it in place during and above all towards the end of the cutting process. If this is not done or is only improperly done, then the weight of the moil will bear on the section of glass or crystal still connecting it to the useful part of the article during cutting, stressing this section and imparting a flexion strain on it which may result in sudden and premature detachment of the moil by a fragile breaking of the glass or crystal section still connecting it to the useful part of the article. Such a break may form a considerably jagged edge or, more generally cause a mechanical deterioration of the edge or bottom of the article produced by the cutting disc; the moil which is detached from the useful part of the article may result in damage to the cutting discs and/or it may be thrown by the discs in an uncontrolled way which could be hazardous for the operator. Similarly, according to this method, the mixture consisting of the cutting liquid charged with powdered glass or crystal will be splashed over the useful part of the article. Furthermore, if the article is hollow and has a fluidtight bottom part, the powder-laden cutting liquid will accumulate in the cavity, perhaps even completely filling it, after which it is necessary either to empty the article before removing it from the machine or to remove it from the machine still filled with cutting liquid. Whatever shape the article is, it is necessary carefully to clean the surface to remove any powdered glass which remains clinging to it. Generally, this cleaning operation is quite time-consuming; it is tiresome to perform the job manually but it is not simple to automate the process, by reason of the wide variety of shapes of such articles.
According to the conventional method of cutting, using an abrasive disc having a substantially horizontal axis of rotation, the weight of the moil which is not supported or is inadequately supported during cutting will bear on the section of glass or crystal which is still connecting the moil to the useful part of the article, stressing it with a composite flexion and shearing stress. This stress, as in the preceding case, may produce sudden and premature detachment of the moil by fragile breakage of the glass or crystal section still connecting it to the useful part of the article. As in the previous case, this break may produce a considerably jagged edge or, more generally, mechanical damage to the edge or bottom of the article produced by the cutting disc; the moil which has just become detached from the useful part of the article may also cause damage to the cutting discs.
If two discs are used, each disc penetrating the article with identical movements, their path during penetration can only be substantially tangential, which in the majority of cases will substantially increase the movement to be performed in order for penetration to be complete. Once penetration is completed, by reason of the penetration of the two discs in accordance with identical movements, the two sections of glass or crystal connecting the moil to the useful part of the article and situated on either side of the furrows caused by the two abrasive discs as they penetrate the article are not identical; that situated in the direction of the original position of the cutting discs prior to penetration will generally be smaller than that which is situated in the opposite direction; therefore, there must be some equalizing phase prior to carrying out the actual cutting process; for this, the article is caused to rotate in the direction opposite to that used for cutting until such time as one of the two discs has, via the groove which it produces during rotation, caused one of the two straight edges of the groove produced during penetration of the two cutting discs, to disappear. Once this operation has been performed, the actual cutting can be carried out fairly rapidly due to the presence of two simultaneously working discs. In this case, the moil which becomes detached from the useful part of the article rests on the two cutting discs; it may result in damage to the cutting discs and/or it may be thrown off by them in an uncontrolled fashion which may be hazardous for the operator.
The trimming or finishing of the edge or bottom of glass or crystal articles is conventionally performed by an abrasive cup wheel of which the axis of rotation is perpendicular or substantially perpendicular to the plane of the edge or of the bottom of the article produced by cutting. As the article is rotating slowly, the grinder is applied to the bottom or edge of the article with a controlled effort; if the grinder has to machine a bottom completely, its abrasive edge will necessarily pass through the centre of rotation of the article; if a more or less thick wall of a hollow article has to be machined, the grinder will be so positioned that its edge is secant to this wall at two quite different places and if possible at two substantially opposite locations.
Maching of the glass or crystal by the cup wheel is carried out at a constant force until such time as the grinder which is penetrating the material comes to bear on a mechanical abutment which is regulated in such a way as to remove an optimum thickness of material.
Generally, the cutting and finishing operations are carried out at different work stations or on different machines.
A machine is already known which employs a cutting device comprising a frame consisting of a base and two columns connected by a cross-member adapted for displacement along the columns and carrying the article carrying head provided with a gripping means, likewise connected by a cross-member generally fixed and equipped with a device for supporting and positioning the tool carrying units. This is the DIAVER type machine built by Messrs. DIAMANT BOART s.a., Avenue du Pont de Luttre 74, B-1190 Forest. This machine carries out the single operation of cutting and employs two discs having substantially vertical axes of rotation, penetrating the article to be cut along identical paths; the article is set on its base on a substantially horizontal table, the part which is hereinabove referred to as the moil constituting the upper part of the mass of glass or crystal constituting the article to be cut.
Also known is a machine which employs cutting and finishing means comprising a frame consisting of a base and two columns connected by a cross-member adapted for displacement along the columns and carrying the article carrying head provided with a gripping means, likewise connected by a cross-member generally fixed and equipped with a device for supporting and positioning the tool carrying units, as well as means for carrying out other associated finishing operations, which is the type 505 machine built by Messrs. W. LINDNER MASCHINEN GmbH, Altenstein 12, D-8352 Grafenau. In the case of the type 505 LINDNER machine, the cutting and finishing operations and the other associated finishing process are performed consecutively at different work stations, each operation being carried out at a single station. Indexing is performed by rotation of the substantially horizontal circular work tab-e on which a plurality of loading stations are provided at equal angular intervals. The article, loaded on its base, is substantially vertical, the part referred to hereinabove as the moil constituting the upper part of the glass or crystal mass which constitutes the article to be cut; the axes of the cutting disc and of the grinders are likewise substantially vertical. The different operations are performed on successive work stations, only the work station on which the operation occupying the most time is performed being permanently in use.